2-Chloroethyl ethyl sulfide (CEES) is a simulant for the chemical warfare agent, bis(2-chloroethyl) sulfide, also known as mustard gas. Here, we demonstrate a facile and rapid method to synthesize a functionalized metal-organic framework (MOF) material for the detection of CEES at trace level. During the synthesis of Zr-BTC, the in situ encapsulation of a fluorescent material (fluorescein) into Zr-BTC voids is performed by a simple solvothermal reaction. The produced F@Zr-BTC is used as a fluorescent probe for CEES detection. The synthesized material shows fluorescence quenching under illumination at an excitation wavelength of 470 nm when F@Zr-BTC is exposed to CEES. This sensing material shows the highest fluorescence quenching at an emission wavelength of 534 nm with a CEES concentration as low as 50 ppb. Therefore, the demonstrated sensing method with F@Zr-BTC is a fast and convenient protocol for the selective and sensitive detection of CEES in practical applications.